1. Field of the Invention
This invention relates generally to a method and apparatus for precisely controlled volumetric injection of selected fluid compositions through a flow control valve for any of a wide variety of purposes. More particularly, the present invention concerns the provision of a flow control valve having relatively movable flow control elements which are capable of cooperatively defining a flow control orifice opening having a valve closed condition blocking the flow of fluid through the valve, a full open condition for allowing maximum flow of fluid through the control valve and wherein the flow port and flow control aperture of the valve cooperate to provide for exponential percent change of the cross-sectional area of the flow control orifice per unit of relative valve element motion. In circumstances where the valve is provided for injection of various fuel additive compositions, the control valve mechanism provides for continuous flow type additive injection, wherein the valve has a very wide range of flow control and has a port design significantly simplifying closed loop control. In particular, as compared to other valves designed for static control, the flow control valve and method of flow control of this invention provides a smooth and continuous controlled change in flow capability per unit change in motion of the movable valve element. In contrast with conventional valve designs wherein the orifice area changes a relatively constant amount per unit increment movement, the wide range valve orifice area of the flow control valve of this invention changes area exponentially per unit increment of movement. The exponential change in area as opposed to linear change in area, permits stable closed-loop control over a very wide flow range. For example, valves with a flow control range of 70,000:1, and a substantially constant percent increment of area per unit increment of movement range of 462:1 have been produced by the inventors according to the teachings of the present invention. Additionally the inventors have developed alternative manufacturing techniques that could extend the flow control range considerably beyond the 70,000:1 control range that the inventors have achieved, which could extend the exponential range to cover substantially the entire flow control range.
2. Description of the Prior Art
Most petroleum based fuels such as gasoline and diesel are required by Federal law to be provided to the end-user only after the addition of certain additives. These additives color or dye untaxed diesel fuel, keep fuel injectors or carburetors clean, reduce or prevent intake valve deposits, or may otherwise enhance the performance as a fuel.
While some of these additives may be introduced at a refinery, or during the transportation process, many are introduced at bulk fuel terminals before the fuel is delivered to a retailer for sale to the end-user. Reasons for introduction at a terminal may be for economic, marketing reasons, or convenience. Each company that sells fuel under its brand name selects a particular additive that suits its marketing objectives and meets any Federally mandated requirements. Bulk (unadditized) fuel is typically supplied to a bulk fuel terminal. Usually, the regular unleaded grade of bulk gasoline is common to all brands sold. A premium grade may be proprietary to a brand or it may support the needs of several brands. For mid-grade, either mid-grade stock or a blend of premium and regular stock may be used. At the terminal, as a truck pulls up to supply the needs for a specific brand, bulk gasoline together with a carefully metered amount of the selected additive is delivered into a compartment on the truck. For a particular brand of product, the amount of additive may be the same for all grades or may vary with the grade. The amounts used typically range from about 0.1 to 1.0 gallon of additive per 1000 gallons of fuel (0.01 to 0.1% by volume).
These additives are made by a number of manufacturers. The additives may vary substantially one from another in viscosity and other flow characteristics as well as chemical constituents. Further, as temperature changes from summer to winter, the viscosity can change widely. The additive flow characteristics can vary from equivalence to gasoline to equivalence to heavy gear lubricant when the temperature ranges from 120.degree. F. to -40.degree. F. In addition to the changes in viscosity, differential pressures can vary as the additive and fuel supply systems support one or a number of active loading stations of a bulk fuel handling facility.
Extensive research has been conducted on various means for introducing precisely metered amounts of additives in liquid form into a fuel stream as it is dispensed from a bulk fuel terminal facility and loaded into a tank truck compartment. A common practice in the industry has been to use a pulse-operated additive injection system based on the use of a solenoid operated valve either to control the number of pulses of fixed volumes of additive or to control the duration of periodic pulses of additive. While these methods are in wide use, their long-term reliability to consistently deliver precise amounts of additive is questionable. The periodic pulsing with fast-rising and fast-falling pressure pulses that occurs in pulse-operated additive injection systems produces repetitive hydraulic shock, known as hydraulic "hammering" throughout the piping system, causing leaks and damage to connected components, such as joints and seals. Cavitation, which may occur under certain conditions, can cause additional system damage. The wide variations in flow characteristics of the various additives cause some of these devices to be operationally incapable of delivering the required precise amounts of additive at all times. These additive materials are relatively expensive. Furthermore, they employ active solvents in order to be able to accomplish their objective. This places severe limitations on the choice of compatible materials. Contamination of the environment from leaks is very undesirable. Excess flow due to leaking seals results in a significant economic loss in addition to potentially introducing amounts of additive that can be significantly in excess of the maximum allowable amounts, amounts that, if used on a consistent basis by motorists, might cause engine damage.
It is desirable therefore to provide an additive injection system that is simple, reliable, and operable with additives that have a wide variation in flow characteristics. It is also desirable to provide a continuous-flow valve having a very wide controllable flow range that is so controlled in its design that stable closed loop control can be reliably achieved.
The amount of fuel that is to be delivered into each compartment on the fuel delivery truck is known. This is preset into a "count-down" counter that terminates the delivery when the preset amount is reached. However, while the preset amount is "known" to the fuel delivery system, it frequently is not available to the additive delivery system. Thus, the additive delivery must be related to the fuel delivery, which is available. The fuel delivery rate is not constant, for many reasons, including varying supply pressures, and the stage of delivery at any load position such as ramping-up and ramping-down high volume product flow. The necessity to maintain an essentially constant ratio of additive to product delivery (constant concentration), with the possibility of premature shutoff for safety reasons, makes it essential to be able to control the additive delivery rate over a significant range. Further, since the additive control valve requires finite time to open, change, and close, these time periods must be factored into the control process to assure a constant additive concentration throughout the fuel delivery process.
In addition to the above, the valve should have the capability of controlling in succession the injection of different additives at different injection rates as brands change for successive product loads.
While a wide flow range can be achieved using a bank of valves of differing flow capabilities, switching from one valve to another can be very difficult to effectively control as the required controlled flow varies from the range of one valve to that of another and back again, changing every few seconds as dynamic pressures of product and additive in a terminal vary.
For smoothness of control, minimum hardware, and minimum system complexity (and thus maximum reliability) it was a principal objective to design a single controllable valve with a very wide flow control range and the ability to smoothly control the opening, modulation, and closing of the valve to eliminate undesirable hydraulic shock, characteristic of pulse operated systems.
Extensive research has suggested several types of flow control valve constructions that held promise as possible candidates. For essentially static operation, where a valve is adjusted to a particular flow capability and essentially left in that configuration for an extended period, a variety of types could be considered. Various concerns regarding reliability, safety, ease of control, and ability to manufacture narrowed the choice. For ease of reliable, consistent closed-loop control, it was desirable for the valve to have an exponential change in flow for a unit increment of movable valve element motion. While analysis suggested how an orifice could be designed to achieve the desired control characteristic, no currently available manufacturing technique was known to have been used to produce it.